The purpose of this manuscript is to share the work of a collaboration between professional development providers and university faculty as they created, implemented and refined a professional development series focused on supporting primary teachers' use of data-based decision making in reading. Using a formative and design-based approach, multiple sources of informal, formative data were collected (surveys, memos and teacher feedback). Data analysis led the team to make refinements to the professional development in response to three broad challenges experienced during Year 1 of implementation. Key refinements made to the professional development series included (1) breaking down the data-based decision making (DBDM) process in reading into more tangible, explicit components (e.g., identifying appropriate assessments, organising and analysing data, using data to target instruction); (2) creating materials tailored specifically to support teachers' knowledge and skills in the DBDM process; and (3) identifying external affordances or barriers to teacher implementation of DBDM (e.g., access to high quality reading assessments and/or intervention materials, communication cycles with other teachers/providers). Challenges experienced and refinements made in this study may provide a framework for thinking about how to support primary teachers to use DBDM in reading and may help administrators understand and reflect on systems-wide factors that may play a role in supporting or hindering teacher enactment of and confidence related to DBDM.